Switching current measurements of large area Josephson tunnel junctions

We have developed a scheme for high resolution measurements of the switching current distribution of a current-biased Josephson tunnel junction using a timing technique. In the measurement setup digital control and read-out electronics are galvanically isolated from the analog sample bias electronics by an optical fiber link. We have successfully used this technique to investigate thermal activation and macroscopic quantum tunneling of the phase in a high-quality 5x5 mum(2) Nb-Al/AlOx-Nb Josephson tunnel junction with a critical current of I(c)approximate to325 muA. At temperatures above the cross over temperature of T(<bstar>)approximate to280 mK the escape is dominated by thermal activation. Due to the high quality factor of the junction (Qapproximate to95), the escape temperature is noticeably affected by the thermal prefactor. At temperatures below T-<bstar>, the value of which agrees well with the theoretical predictions, the escape of the phase by quantum mechanical tunneling is observed. The presented technique can be employed to characterize current-biased Josephson tunnel junctions for applications in quantum information processing. (C) 2003 American Institute of Physics.